1. Field of the Invention
The present invention relates to a method of monitoring the behavior of carbon dioxide put into a layer of submarine sandstone by using the marine Controlled-Sources Electromagnetic (“CSEM”) survey. More particularly, the present invention relates to a method of monitoring the behavior of carbon dioxide in a layer of sandstone by analyzing a value of marine CSEM and using the variation in the amplitude of an electric field and the phase difference before and after charging carbon dioxide, when arising an electrical resistivity with charging carbon dioxide into a layer of sandstone which is saturated with salt water. According to the present invention, Archie's empirical formula can be induced by measuring an electrical resistivity after saturating a sandstone taken from a subterranean level submarine with various solutions having different NaCl concentrations, and then an empirical formula can be established, which can be used for the calculation of an electrical resistivity according to an amount of carbon dioxide charged into a layer of sandstone. Also, according to the present invention, a simple geological stratum model can be established, which includes a porous sandstone suitable for storing carbon dioxide under the ground and shale of an impermeable layer which covers the sandstone layer, and to calculate an inputting value of an electrical resistivity for a layer of sandstone according to an amount of carbon dioxide put into a layer of sandstone.
2. Description of the Prior Art
In storing CO2 under the ground to reduce a greenhouse gas, it is important to develop a technique of monitoring the behavior of CO2. At laboratory and pilot site the electrical resistivity and the seismic wave velocity are being used. However, there has been no proposed monitoring technique or monitoring method in relation to the storing of CO2 under the marine ground, other then the seismic survey.
Considering the characteristics of stratum and a geological structure of the pilot site for storing CO2 under the ground located at the district of Nagaoka, Japan and Ketzin, Germany, the layer of sandstone which is an object for charging CO2 has a porosity above 20%, and this layer is covered with a shale having a low permeability so that it has a geological condition which does not leak CO2 after charging (Andrea Forster et al., 2006; Xue, et al., 2006). Korean continental shelf has similar characteristics of stratum and geological structure with the above-mentioned district. Thus, there is a possibility for storing CO2 under the ground through analyzing a data of geophysical surveys and drilling search for the Korean continental shelf.
To make a practical technique for storing CO2 under the ground, above all, it should be able to measure a storing potential and a behavior of CO2 charged under the ground. Various experiments at a pilot site and lab experiments have been carried out to the purpose mentioned above.
Indoor experiment may be carried out by monitoring the behavior and the charged amount by using an increase of electrical resistivity and a reduction of seismic wave velocity according to the charged amount of carbon dioxide through measurement of electrical resistivity and seismic wave velocity at the time before and after charging carbon dioxide into a layer of sandstone (Onishi, et al., 2006; Xue and Lei, 2006). Also, experiment at pilot site may be carried out by monitoring the behavior of CO2 under the ground by using either seismic wave tomography survey, or various monitoring technique for exploration such as gravity prospecting and well logging (Xue, et al., 2006; Saito et al., 2006; Sherlock et al., 2006).
Among these methods for exploration, the tomography survey which uses a seismic wave and an electrical resistivity is proposed as useful method in analyzing the behavior of CO2 under the ground due to its high solution capacity for a result of exploration, even though there is a difficulty in using an exploratory hole.
Since the approach for the method of an electrical resistivity and a seismic wave tomography survey is not easy in storing CO2 under the marine ground, the example using marine seismic survey has been reported (Chadwick, et al., 2009). However, seismic survey has a drawback in that it is difficult to measure a charged amount quantitatively because velocity reduction is not incurred corresponding to the increase of a charged CO2 amount, even though it is advantageous for analyzing a charging range with inducing a large reduction of velocity before and after charging carbon dioxide.
On the other hand, since an electrical resistivity is continuously increased either at the time before and after charging carbon dioxide, or upon to increase of a charged amount so that it is easy to measure a charging range of CO2 as well as a charged amount quantitatively, it is necessary to review the adaptability of Marine CSEM.